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<h1 class="title">扩展QML -扩展对象示例</h1>
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<p>扩展对象。</p>
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<p>这个例子建立在:</p>
<ul>
<li><a href="qtqml-referenceexamples-adding-example.html">扩展QML -添加类型示例</a></li>
</ul>
<p>演示如何使用<a href="qqmlengine.html#qmlRegisterExtendedType">qmlRegisterExtendedType()</a>为<a href="../qtwidgets/qlineedit.html">QLineEdit</a>提供<a href="qtqml-cppintegration-definetypes.html#registering-extension-objects">扩展对象</a>，而无需修改或子类化它。</p>
<p>首先，LineEditExtension类作为<a href="../qtwidgets/qlineedit.html">QLineEdit</a>的扩展在QML系统中注册:</p>
<pre class="cpp">

      qmlRegisterExtendedType<span class="operator">&lt;</span><span class="type"><a href="../qtwidgets/qlineedit.html">QLineEdit</a></span><span class="operator">,</span> LineEditExtension<span class="operator">&gt;</span>(<span class="string">&quot;People&quot;</span><span class="operator">,</span> <span class="number">1</span><span class="operator">,</span><span class="number">0</span><span class="operator">,</span> <span class="string">&quot;QLineEdit&quot;</span>);

</pre>
<p>QML引擎然后实例化一个<a href="../qtwidgets/qlineedit.html">QLineEdit</a>:</p>
<pre class="cpp">

      <span class="type"><a href="qqmlengine.html">QQmlEngine</a></span> engine;
      <span class="type"><a href="qqmlcomponent.html">QQmlComponent</a></span> component(<span class="operator">&amp;</span>engine<span class="operator">,</span> <span class="type"><a href="../qtcore/qurl.html">QUrl</a></span>(<span class="string">&quot;qrc:example.qml&quot;</span>));
      <span class="type"><a href="../qtwidgets/qlineedit.html">QLineEdit</a></span> <span class="operator">*</span>edit <span class="operator">=</span> qobject_cast<span class="operator">&lt;</span><span class="type"><a href="../qtwidgets/qlineedit.html">QLineEdit</a></span> <span class="operator">*</span><span class="operator">&gt;</span>(component<span class="operator">.</span>create());

</pre>
<p>在QML中，在LineEditExtension类中只存在的行编辑中设置了一个属性:</p>
<pre class="qml">

  <span class="type">QLineEdit</span> {
      <span class="name">leftMargin</span>: <span class="number">20</span>
  }

</pre>
<p>扩展类型对<a href="../qtwidgets/qlineedit.html">QLineEdit</a>执行调用，否则QML引擎将无法访问这些调用。</p>
<p><span lang="zh-cn">文件：</span></p>
<ul>
<li><a href="qtqml-referenceexamples-extended-example-qml.html">referenceexamples/extended/example.qml</a></li>
<li><a href="qtqml-referenceexamples-extended-extended-pro.html">referenceexamples/extended/extended.pro</a></li>
<li><a href="qtqml-referenceexamples-extended-extended-qrc.html">referenceexamples/extended/extended.qrc</a></li>
<li><a href="qtqml-referenceexamples-extended-lineedit-cpp.html">referenceexamples/extended/lineedit.cpp</a></li>
<li><a href="qtqml-referenceexamples-extended-lineedit-h.html">referenceexamples/extended/lineedit.h</a></li>
<li><a href="qtqml-referenceexamples-extended-main-cpp.html">referenceexamples/extended/main.cpp</a></li>
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